The invention relates to a mobile radio system having at least two mobile radio regions.
In accordance with international standards, mobile radio systems are available having open interfaces which allow a combination of functional devices--exchanges, data banks, radio devices, etc--from different manufacturers. Outgoing and incoming telephone calls can be made everywhere in the mobile radio system, using one and the same mobile station, by means of a standard air interface for the wire-free link from the mobile stations of mobile subscribers to base station systems. A precondition for such a mobile radio system is a system of signaling links which is compatible throughout, in order to make it possible to transmit control information and data--as the generic term for all telecommunications signals which can be transmitted in the mobile radio system, such as voice signals, data signals etc--between the functional devices of the system.
As a result of the international standardization which is applicable to Europe, signaling protocols in accordance with the "Central Character System No. 7 (CCS7)" are used, for example, for these signaling links in a GSM mobile radio system (Global System for Mobile Communication). Corresponding standards are also available in the USA and other countries and continents. In consequence, it is possible for mutually incompatible signaling protocols to exist in a mobile radio system having at least two mobile radio regions--for example Europe and the USA. The mobile radio systems which exist in the various mobile radio regions are, in contrast, compatible with one another, that is to say similar subscriber data exist for designation of the mobile subscribers, and corresponding subscriber services. The problem of incompatible signaling protocols will be indicated using the example of the "roaming function" in the mobile radio system. Assuming that a mobile station which is served by a transmitting/receiving station of a base station system arranged in a first mobile radio region moves into the area of a transmitting/receiving station of a new base station system in a second mobile radio region ("roaming"), the subscriber data assigned to the mobile station by the home register of the first mobile radio region would have to be transmitted to the visitor register, which is linked to the new base system, of the second mobile radio region, and be stored there, when setting up a radio contact in the new region. The subscriber data which are stored in the last responsible visitor register of the first mobile radio region are deleted, and the address of the new visitor register is stored in the home register. It would be necessary to change from one signaling protocol to the other in order to carry out these data operations. The mobile subscriber, including his mobile station, is always entered with the associated subscriber data in only one home register and, at any time, in only a single visitor register which is currently responsible for the mobile subscriber.
Setting up and clearing connections between the home register and the respectively related visitor register, and the interchange of data and control information, are highly complex and require a powerful signaling protocol. If, as indicated above, the registers are located in at least two mobile radio regions having mutually incompatible signaling protocols, a translation function would be necessary for the transition between the mobile radio regions, or the functional devices of the mobile radio system would themselves have to cope with a plurality of such protocols. In any case, such an implementation of a mobile radio system having a plurality of mobile radio regions in which incompatible signaling protocols exist requires a high level of complexity when transferring the mobile station from a first mobile radio region to a second mobile radio region.